To satisfy researchers' demands for more information about their compounds of interest, manufacturers of HPLC, UHPLC, LC/MS and GC/MS systems are constantly developing new technologies that lower the detection limits of these separation systems. Accompanying these ever decreasing detection limits is the need for higher purity samples and cleaner mobile phases. Samples and buffers, after proper filtration, not only generate higher quality, more consistent results, they also increase instrument uptime and prolong column life.
One conventional sample preparation device for chromatography applications is a Millex® filter, commercially available from Millipore Corporation. These filters are non-sterile, low-extractable filters for clarification or fine particulate removal prior to instrument analysis. Millex® filter units contain a membrane in a housing, such as a high density polyethylene or polypropylene housing. One or more filter layers are permanently sealed between two plastic filter holder halves, the first half having an inlet port and the second half having an outlet port. The outer peripheral edge of the membrane is trapped between the two halves. The outer peripheral edges and of the two halves can be sealed together by an overmold of plastic to form a liquid tightly sealed device. A variety of membranes and housings ensure chemical compatibility with a range of samples and solvents. For example, Millex®-LCR filters contain a hydrophilic PTFE membrane and are HPLC-certified for low levels of UV-absorbing extractables, and provide a very clean sample for HPLC analysis. Durapore® (PVDF) filters combine fast flow with low protein binding. Nylon filters provide broad chemical compatibility for use with aqueous and organic solutions. Millipore Express® PLUS (PES) filters have high flow rates and higher throughput. MF-Millipore™ mixed cellulose ester (MCE) membrane is a widely used, general purpose filter. Glass fiber can be used for clarifying aqueous or organic solutions with high particulate levels and can also be present in the housing as a prefilter. Depending on process volume, filter sizes range from 4 mm to 33 mm in diameter. The Millex® filters are used in conjunction with pressure driven hand-held syringes.
It would be desirable to increase the speed and ease the preparation of one or more samples for applications such as HPLC analysis, while reducing the occurrence of human error, the repetitive motion and duration of the applied load necessary to operate hand-held devices, and the presence of contaminants.